1. Field of the Invention
The present invention relates to power plants. More specifically, the present invention relates to methods and apparatus for a pinwheel power plant that employs solid fuel propellant.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art
Many different types of power plants are known in the art for providing thrust to propel a projectile. Examples include jet engines, piston engines and rocket motors of various designs. Each of these power plant designs suffer from a number of problems during the launch and flight stages of the projectile. The problems common to each power plant design include the generation of excessive noise and heat. Also, in the case of a rocket motor, large amounts of smoke can be generated.
Low detectability of a projectile during target approach is necessary in stealth operations. However, the generation of excessive noise during the launch and flight stages increases the probability that the projectile will be detected upon approach. Further, generation of large amounts of heat by the projectile motor can be detected by infrared sensors such as the forward looking infrared devices utilized by deployed ground troops and aircraft. The heat generated by the projectile motor can also be detected visually by utilizing night vision goggles. Likewise, the projectile can also produce a visible smoke trail. The visible smoke trail generated by certain rocket motors facilitates tracking the projectile and enables the determination of the origin of the launch point. The density of the smoke trail is dependent upon the type of rocket motor propellant employed. Each of these problems increase the probability of projectile detection during approach to the target.
Specific examples of power plant designs capable of providing thrust to propel a projectile include solid and liquid fueled rocket motors, air turbo rockets and jet turbine engines. Solid fuel rocket motors employing solid fuel propellants are known. The solid fuel propellant of certain rocket fuel motors burns at an accelerated rate producing a pressurized exhaust gas. The pressurized exhaust gas is then expelled from an exhaust nozzle at a supersonic rate to propel the projectile. The expanding gas exiting the exhaust nozzle is very noisy, generates excessive heat and creates a characteristic IR signature. In general, the burn rate of the solid fuel propellant is determined by the configuration of the solid fuel element employed. The amount of surface area of the solid fuel propellant exposed to burning determines the gas pressure generated. The more surface area of the solid fuel propellant exposed to burning, the higher the gas pressure generated. Solid fuel propellants having a large surface area exposed to burning tend to burn much faster. The generation of excessive noise, heat and smoke by the solid fuel rocket tend to increase the detectability of the projectile.
The second example of a power plant design capable of providing thrust to propel a projectile is an air turbo rocket. An air turbo rocket, which is known in the art, is capable of burning solid or liquid fuel to drive a turbine or compressor. The operation of the turbine or compressor produces increased gas pressure in an exhaust tube. When ambient air is funneled into the exhaust section of the air turbo rocket, the fuel is reignited and burned. This design effectively operates as an after burner. Because of the after burner effect, air turbo rockets are very noisy and are subject to audible detection. Liquid fuel is also utilized to provide thrust in other power plants such as in jet turbine engines, liquid fuel rocket motors and piston engines. Numerous problems exist when attempting to contain liquid jet fuel in a fuel tank on a projectile. The utility and purity of the liquid jet fuel can be effected by the elements and by contamination. Additionally, the heavy mass of the liquid fuel adds to the load of the projectile during flight. Further, as the liquid fuel is consumed, the dynamics of the projectile are altered.
Unfortunately, the generation of excessive noise and heat tend to make the projectile power plant designs of the prior art vulnerable to detection by audible and infrared devices. Further, the creation of a visible smoke trail also causes the projectile to be easier to track. Therefore, the power plants of the prior art which are designed for use with a projectile are vulnerable to detection and are not suitable for use in stealth operations.
A final example of a power plant known in the art that employs solid fuel propellant is a pinwheel motor. A pinwheel motor is generally toroidal or ring shaped and is designed to rotate about a central axis passing through the center thereof. The ring shaped pinwheel is constructed to include a plurality of compartments formed therein with each adjacent compartment being spaced apart by a separation zone. Each compartment houses a solid fuel stick and each solid fuel stick includes a fuse which is inserted in the respective separation zone. The fuse ignites the solid fuel propellant by a known method and the fuse is burnt. Once the fuse for a particular compartment is burnt, the separation zone associated with that compartment becomes the exhaust port for that compartment. The solid fuel propellant in each compartment is thereafter combusted at a specified rate generating a high pressure exhaust gas. The high pressure gas is exhausted to atmosphere from each compartment through the respective exhaust port. The exhaust from the multiple exhaust ports cause the pinwheel to spin about the central axis. Generally, the pinwheel motor does not drive a load or propel a projectile but is employed in pyrotechnic displays.
Thus, there is a need in the art for improvements in solid fuel pinwheel power plant designs for use with a projectile which exhibit the characteristic of low detectability and are suitable for use in stealth operations.